1. Field of the Invention
The present invention relates to an electron beam exposure method, more particularly to a method for correcting a proximity effect, an exposure method using the methodology for correcting a proximity effect, a manufacturing method of a semiconductor device and a proximity correction module.
2. Description of the Related Art
Photolithography has been widely used in manufacturing of a semiconductor device such as a large scale integrated circuit (LSI) because of its advantages such as process simplicity and low cost. Technological innovations in photolithography have been constantly carried out. In recent years, by shortening a wavelength of a light source such as an argon fluoride (ArF) excimer laser, miniaturization of an element to a level of 0.1 xcexcm has been achieved. In an attempt to further advance the miniaturization, development of an exposure apparatus using a fluorine gas (F2) excimer laser with a shorter wavelength has been undertaken. The exposure apparatus using a shorter wavelength is expected as a mass production lithography tool in response to a 70 nm rule generation. However, there are many problems to be solved in order to realize such exposure apparatus and the development period has been prolonged. Consequently, there is concern that the development of the exposure apparatus cannot catch up with the speed of the miniaturization of the semiconductor device.
As a countermeasure for the above problem, in the field of an lectron beam (EB) lithography, it is verified that processing as minute as 10 nm is possible by use of a narrow electron beam. From the viewpoint of miniaturization, there seems to be no problem at the moment. However, regarding a dimensional accuracy of a delineated pattern, there is a problem, a so-called xe2x80x9cproximity effect,xe2x80x9d in which a finished size of the pattern varies depending on a pattern area density,
When an electron beam is irradiated on a substrate for exposure, electrons expose a resist film while scattering inside the resist film. Thereafter, the electrons cause elastic scattering by colliding with a substrate material and are reflected. The reflection is called backward scattering and the reflected electrons are called backscattered electrons. The backscattered electrons expose the resist by being made incident on the resist again from the substrate. In this vent, a distribution of energies accumulated in the resist film is approximately expressed by the sum of Gaussian distributions as below.
f(r)={exp(xe2x88x92r2/xcex2f2)/xcex2f2+xcex7*exp(xe2x88x92r2/xcex2b2)/xcex2b2})/(1+xcex7)xe2x80x83xe2x80x83(1)
Here, r is a distance from an electron beam irradiation position, xcex2f is a forward scattering distance, xcex2b is a backward scattering distance and xcex7 is a ratio of a backscattered energy to an irradiation energy. The first term in the right side represents the forward scattered electrons and the second term in the right side represents a distribution of the backscattered electrons.
The problem here is the point that regions other than the position irradiated by the electron beam are subjected to exposure by the backscattered electrons. In other words, the resist film at the position irradiated by the electron beam is exposed not only by the incident electrons but also by the backscattered electrons in subjecting a surrounding pattern to the exposure. As a result, energies accumulated in the resist film are distributed depending on a surrounding pattern area density, thus causing a distribution in a finished size of a resist pattern after development. This is called the proximity effect.
A backscatter radius is at the same level as the backscattering distance xcex2b. When focusing attention on a small region narrower than this region, an accumulated energy "Egr"b in the resist due to backscattered electrons in the small region is approximately in proportion to a processing pattern area density xcex1 and is expressed as below.
xe2x80x83"Egr"b=C*xcex7*xcex1*Dxe2x80x83xe2x80x83(2)
Here, C is a constant and D is an irradiation energy (dose).
Therefore, by correcting the dose D in accordance with the processing pattern area density xcex1, the size of the resist pattern can be controlled. The following equation is an example of a dose correction equation in the case of a uniform film structure of a substrate.
D=C/(xc2xd+xcex7*xcex1)xe2x80x83xe2x80x83(3)
However, during the EB lithography in an actual LSI manufacturing process, there exists an underlying layer having a structure of an underlying pattern provided on a silicon (Si) substrate. Specifically, a material of the underlying pattern differs depending on a position of irradiating an electron beam and thus an energy intensity distribution of backscattered electrons changes depending on the material of the underlying pattern. Accordingly, it is necessary to correct an incident energy in consideration of the presence of not only a processing pattern but also the underlying pattern. Consequently, the earlier correction is performed by use of the following equation disclosed in xe2x80x9cJournal of Vacuum Science Technologyxe2x80x9d (F. Murai, et al., J. Vac. Sci. Technol. B10, 3072, 1992).
D=C/{xc2xd+xcex7*[xcex1+(xcex71/xcex7xe2x88x921)*xcex1*xcex110]}xe2x80x83xe2x80x83(4)
Note that xcex110 is an underlying pattern area density of an underlying layer and xcex71 is a ratio of a backscattered energy to an incident energy of an underlying pattern material.
However, the correction equation (4) hypothesizes that an area ratio of a pattern delineated on the underlying pattern among the delineating pattern region is equivalent to the underlying pattern area density xcex110 in a unit region. It is assumed that a processing pattern 30 of a pattern area density xcex1 as shown in FIG. 1 is exposed on a semiconductor substrate having an underlying pattern 32 of the underlying pattern area density xcex110 shown in FIG. 2. When the processing pattern 30 overlaps with the underlying pattern 32, as shown in FIG. 3, the underlying pattern area density xcex110 for the unit region is different from an underlying pattern area density under the processing pattern 30 actually exposed on the semiconductor substrate having the underlying pattern 32. Therefore, by use of the earlier correction equation using the underlying pattern area density xcex110, a sufficient correction accuracy cannot be achieved.
A first aspect of the present invention inheres in a method for correcting a proximity effect, and includes: classifying an underlying pattern of a level underlying a thin film layer; dividing a processing pattern to be transferred on the thin film layer into a first pattern overlapping with the underlying pattern and a second pattern which does not overlap with the underlying pattern according to the classified underlying pattern: calculating a pattern area density for the first and second patterns in a unit region; and calculating a corrected dose for the processing pattern according to the pattern area density.
A second aspect of the present invention inheres in an exposure method, and includes: preparing a substrate having a thin film layer deposited on a surface of an underlying layer, the underlying layer having an underlying pattern; coating a resist film on the thin film layer; obtaining a processing pattern configured to delineate on the resist film, and the underlying pattern; classifying the underlying pattern; dividing the processing pattern into a first pattern which overlaps with the underlying pattern and a second pattern which does not overlap with the underlying pattern, according to the classified underlying pattern; calculating a pattern area density for the first and second patterns in a unit region; calculating a corrected dose for the processing pattern based on the pattern area density; and exposing the resist film by the corrected dose.
A third aspect of the present invention inheres in a manufacturing method of a semiconductor device, and includes: forming an underlying pattern of an underlying layer on a semiconductor substrate; depositing a thin film layer in a surface of the underlying layer; coating a resist film on the thin film layer; loading the semiconductor substrate on a movable stage of an electron beam exposure apparatus; calculating a corrected dose by the steps of classifying the underlying pattern, dividing a processing pattern to be delineated on the resist film into an first pattern which overlaps with the underlying pattern and a second pattern which does not overlap with the underlying pattern according to the classified underlying pattern, calculating a pattern area density for the first and second patterns in a unit region, and calculating a corrected dose for the processing pattern based on the pattern area density; exposing the resist film by the corrected dose; developing the resist film; and processing the thin film layer by use of the developed resist film as a mask and transferring the processing pattern onto the thin film layer.
A fourth aspect of the present invention inheres in a proximity correction module, and includes: an area density calculation unit configured to classify an underlying pattern of an underlying layer, to divide a processing pattern to be delineated on a thin film layer formed in a surface of the underlying layer according to the classified underlying pattern into a pattern overlapping with the underlying pattern and a pattern not overlapping therewith and to calculate a pattern area density for each of the divided processing patterns in a unit region; an area density map memory configured to store a position of the unit region and the pattern area density of each of the divided processing patterns; and a dose correction calculation unit configured to calculate a corrected dose for the processing pattern based on the pattern area density.